Calutron



A. F. CLARK June 16, 1959 CALUTRON 3 Sheets-Sheet 1 Filed Sept. 20, 1946 INVENTOR. ARA/0L0 f CLARK 4 ATTORNEY June 16, 1959 A. F. CLARK 2,891,163

CALUTRON Filed Sept. 20, 1946 5 Sheets-Sheet 2 ARA/0L0 F CLARK BY w M ATTORNEY A. F. CLARK CALUTRON June 16, 1959 Filed Sept. 20, 1946 956/0 0/ b OSC/LLAT/A/G ELECTRON? 3 Sheets-Sheet '3 J42 INVENTCR.

+ 6 ARNOLD F. CLARK ATTORNEY.

Unite Sttes Patent CALUTRON Arnold F. Clark, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application September 20, 1946, Serial No. 698,335 (Ilaims. (Cl. 250-419) This invention relates to calutrons and more partic: ularly to means for eliminating oscillating electrons from the arc slit region of a multiple ion generator calutron ion source.

Calutrons are described in general in Atomic Energy for Military Purposes, by H. D. Smyth, and in great detail in US. Patent No. 2,709,222, issued to Ernest 0. Lawrence, on March 24, 1955. Calutrons have been principally employed and very successfully employed in separating the isotopes of uranium for military energy purposes. In general, ions of a polyisotopic mixture of a desired element are formed and projected into a magnetic field. Thereafter, the ions travel in curved paths, the ions of greater mass describing flatter curves than the ions of lesser mass. path, preferably at the 180 in each curve. The ions are there neutralized and collected substantially separatedfrom ions of difierent mass.

In the commercial form of calutrons, it is customary to have a single source unit that has several ion generators, each having its own ion exit slit or arc slit. When an ion beam is projected outwardly from an arc slit, it bombards molecules of the ambient atmosphere within the vacuum tank of the calutron. This bombardment forms positive ions and free electrons in the atmosphere and it is the free electrons thus generated with which the present invention deals. These electrons are attracted toward the highly positive ion generators but the prevailing magnetic field causes them to follow a scalloped path along the equipotential lines. In a multiple ion generator unit, the electrons thus freed in the region of one ion generator travel across the ion beam of the adjoining ion generator interfering with this beam and giving rise to the multiplication of electrons thus causing a fluctuating condition of the ion beam. This fluctuating ion beam is very undesirable, interfering with the separating action and reducing the ion current in the beam.

The present invention eliminates the undue multiplication of electrons resulting from the interaction of free electrons with the ion beam by guiding the free electrons to a region Where they may be dumped, that is, dis charged. They are thereby completely eliminated and thus the ion source is completely freed from the deleterious effect of these electrons.

It is, therefore, an object of the invention to provide a calutron ion source that is free from the effects of electrons on the ion beam.

Another object of the invention is to provide an electron dump between the arc slits of a multiple ion generator. source unit for the elimination of free electrons.

Another object of the invention is to provide an electron dump between the arc slits of a multiple ion generator source unit in order to minimize the multiplication of electrons. i

Other objects and advantages of the invention will be apparent in the following description and claims considered together with the accompanying drawings, in which:

Suitable collectors are placed along each Figure 1 is a schematic plan view taken along a magnetically transverse plane of a multiple ion generator, calutron and showing the electron paths in the absence. of the present invention;

Fig. 2 is an elevation front view of the ion source of Fig. 1 with the dumps of the present invention applied thereto;

Fig. 3 is. a top View of the ion source of Fig. 2;

Fig. 4 is a side view in section taken along the line. 4 4 of Fig. 2;

Fig. 5 is an elevation view of one of the dumping. fins made in accordance with the present invention; and

Fig. 6 is an enlarged sectional View taken along the line 6-6 of Fig. 4.

Referring to Fig. 1, there is illustrated a vacuum tank 10 having a connecting conduit 11 attached to a pump 12, for evacuating the tank to a suitable degree, such as l() or 10- mm. Hg. A magnetic field permeates the entire vacuum tank as indicated by the cross lines 13. Secured to an inner wall of the vacuum tank 10 is insulator 14 having a plate 16 secured on the inner end thereof and to which is secured a plurality of ion generators 17 designated as #1, #2, #3 and #4. The ion forming mechanism is an arc discharge which takes place in the ion generators 17 and the ions formed therein leave the ion generators 17 through an arc slit 18 in each ion generator.

Disposed opposite each arc slit 18 is a pair of accelerating electrodes 19 and a second pair of decelerating elec: trodes 21. The ion generators 17 are maintained at a high positive potential and the accelerating electrodes 19 are maintained at a high negative potential. The resulting: electric field is indicated by equipotential lines 22 and is highly negative to extract the positive ions from the ion generators 17. This electric field is much stronger than desired for the allowable radius of curvature of the ion paths in order to obtain a greater ion current. Accordingly, the decelerating electrodes 21 are provided and maintained at ground potential which is positive with respect to the negative potential on the electrodes 19.. This relatively positive potential on the electrodes 21 slows up the ions, causing them to travel in curves of smaller, radius than would otherwise be the case.

The ion beams emanating from the arc slits 18 are generally designated by the numeral 23 and thereafter split into two separate beams 23a and 23b for the U235. and U components, respectively. Collectors 24 are suitably disposed at the point in the curved path of travel of the beams and are divided into a U 5 pocket 26 and a U pocket 27 which collect the respective beam components which enter through apertures 28 and 29. The ions are discharged in these pockets and after a run of suitable duration, the collectors are scraped to remove the monoisotopic metal therefrom. Collectors #1, #2, #3 and #4 receive the ion beam from the corre:

spondingly numbered ion generators.

As previously mentioned, the ion beam 23 bombards the ambient atmosphere within the vacuum tank 10, creating positive ions of the gas molecules and free electrons. These free electrons that are generated in the space between the arc slit 18 and the accelerating electrodes 19 are attracted toward the ion generators 17. The magnetic field 13, however, prevents them from travelling directly toward the ion generator 17 and their magnetically trans; verse paths take the form of scalloped paths 31. At the same time the electrons are migrating in the scalloped paths, they are also in violent oscillation along the magnetic field because of the crossed electric and magnetic fields encountered at the top and bottom of the ion generators 17. These oscillating electrons travelling along. scalloped paths 31 cause the multiplication of electrons? and'then cross the ion beams'23 emanating from the next Patented June 16, 1959;

succeeding ion generator and seriously interfere with the operation of the calutron.

Referring to Figs. 2 and 3, there is shown the ion generators 17 with their respective arc slits 18. I provide, however, between each arc slit 18, an angular recess32 in theshape of a W standing on edge. Fitted into this W-shaped recess is a similarly shaped fin 33 supported by and at the same potential as the decelerating electrodes 21. 'As shown in 'Fig. 2, the combination of the recess and the fins sets up a fin and blister, as described in U. S. Patent No. 2,727,150, issued to Ernest 0. Lawrence, on December 13, 1955, which limitsthe region in which the electrons may oscillate. Further, by reference to Fig. 4, it will be noted that the back end of the recess 32 is not planar but rather has projections 34 near the top and bottom to a corresponding depression 36 therebetween. The fin 33 in this region is similarly contoured and has relieved portions 37 opposite the projecting portions 34. This construction also sets up a fin and blister effect at the bottom end or rear of the recess 32 and the fin 33.

This fin and blister eifect results from the fact that there are crossed electric and magnetic fields. As shown inFig. 2, the fin 33 is highly negative with respect to the ion generators 1'7 and the grooves 32 formed therein. The electrons are attracted toward projecting points 38 of the recess 32 because these points are positive. The magnetic field, however, constrains the electrons to movement along the magnetic field resulting in oscillation in the shaded regions 39. The fin and blister effect, therefore, limits the volume within which the electrons may oscillate and thus is a notable step forward in eliminating the effect of oscillating electrons from the whole region between the arc slits 18 and the accelerating electrodes 19.

The electrons continue to migrate during their oscillating course, however, and the direction of this migration is shown by the arrows in Fig. 6. As previously described with respect to Fig. 4, the conditions are maintained at the bottom of the groove 32 to continue the fin and blister effect and therefore the oscillations, the region of oscillation being indicated in Fig. 4 also by the numeral 39.

Referring to Fig. 2, however, it will be noted that when the electrons migrate completely around the bottom or innermost end of the fin 33 that they reach a region where the crossed electric and magnetic fields no longer permit oscillation to take place. Rather, the electric field is reversed, thereby effectively suppressing oscillations and causing the electrons to travel toward a nearby positive point and become discharged. This region of discharge is indicated by the shaded area 44. The basic structure of this effect is disclosed in the abandoned application of Edward J. Lofgren, Serial No. 698,339, filed September 20, 1946. It will be noted that the fin 33 in Fig. 2 has projecting portions 41 matched by similarly relieved portions 42 on the groove 32, the fin being negative'with respect to the positive side walls of the groove 32. The electrons are repelled away from the fin bulge 41 toward the walls of th groove 32 and thereupon become discharged. The electric fields in this region are reversed from those necessary to cause oscillation, as previously noted. Thus, the electrons are completely removed from the region between the arc slits 18 and the accelerating electrodes 19. Suitable heaters 43 may be provided to heat the fins 33 to prevent condensation of vapor thereupon.

The operation is best explained with reference to Figs. 2, 3 and 4 and with reference to a single fin and recess although the other .fins and recesses operate similarly. The ion beams 23 emanating from the arc slits 18 bombard the ambient atmosphere, releasing free electrons in the region between the arc slit 18 and the accelerating electrodes 19. These electrons tend to follow scalloped paths toward the receiver while at the same time oscillating violently along the magnetic field. They encounter, however, the electric field set up by the fins 33 and thereupon travel parallel to the surface of the fins 33 toward the recess 32. Due to the configuration of the fin 33 and its recess 32, a fin and blister efiect is set up which limits the oscillation to the regions 39 indicated in Fig. 2. The oscillating electrons migrate around to the end of the fin 33, as indicated in Fig. 4. When they pass the end of the fin 33, they encounter reversed electric fields, as indicated in Fig. 2, and thereupon dump to the positive side walls of the groove 32, as indicated by the shaded area 44 in Fig. 2. T he electrons being discharged are completely eliminated.

Although this invention has been described with reference to a particular embodiment thereof, it is not limited to this embodiment nor otherwise except by the terms of the following claims.

What is claimed is:

1. In a calutron, means for establishing a magnetic field, a vacuum tank disposed therein maintained at a fixed potential, an ion generator insulatedly mounted in the tank and maintained at a positive potential relative.

thereto and including a plurality of open-sided arc cavities, electrode means disposed opposite the arc cavities for withdrawing positive ions from the arc cavities, and

a bent fin projecting into the space between the arcs and.

maintained at a negative potential relative to the ion generator and positioned with respect to the magnetic field a V-shaped fin positioned between the cavity openings and.

disposed with respect to the magnetic field so that a common portion of the field passes through both sides, and

the V-shaped fin lying in a plane passing through two are openings, the thickness of the fin in the direction of ion flow being smallest at the apex of the V-shaped fin, the ion generator having a recess into which the fin projects in spaced relation.

3. In a calutron, means for establishing a magnetic field, a vacuum tank disposed therein and maintained at ground potential, an ion source unit insulatedly mounted in the tank and maintained at a positive potential and including a plurality of arc cavities having exterior openings, and having recesses disposed between the arc cavity openings, and W-shaped fins maintained at a negative.

potential and projecting into the cavities and disposed with respect to the magnetic field so that all portions of the fin are traversed by substantially the same magnetic field.

4. A calutron comprising, means for establishing a magnetic field, an ion source unit including a plurality of ion generators each having an ion exit slit, accelerating electrodes disposed opposite the ion exit slits, means forming a groove in the ion source unit between two adjacent ion exit slits and having an intermediate portion of the bottom thereof projecting toward the accelerating electrodes, and a curved fin maintained at the potential of the decelerating electrodes and fitting within but spaced from the groove, said fin being disposed with common projections of said magnetic field forming chords of the curve of said fin.

5. In a calutron including means for establishing a magnetic field, an ion generator maintained at a positive potential and having ion exit slits parallel to said magnetic field, and negatively charged ion accelerating electrodes disposed adjacent said ion egress apertures; means.

to neutralize free electrons produced exterior to said ion generator and oscillating under the influence of said electiic arid magnetic fields toward said ion generator, intions of said magnetic field lying on chords of the curves eluding depressions upon the face of said ion generator thereof, thereby defining regions of restricted electron osadjacent said ion exit slits, and fins of a similar configuracillation and contiguous regions of reversed electric fields tion as said depressions disposed within said dejiress'ions whereby eiectrons attracted thereto impinge upon said and at a negative potential with respect to said ion gen- 8 ion generator and are neutralized; rator, said fins being curved in two planes at right an- 'gles to each other and disj osed with common projec- No references cited. 

